Abstract
Previous studies have shown that d- arabino-2-hexulose (trivial name, d-glucosone) is converted to l-ascorbic acid in bean and spinach leaves. The present study examines oxidative cleavage of l-ascorbic acid to oxalic acid and l-tartaric acid in detached leaves of Pelargonium crispum supplied with d-[5- 3H,1- 14C]- or d-[5- 3H,6- 14C]glucosone. Labelled leaves were analysed for distribution of 14C and 3H among soluble and insoluble constituents. d-Glucose (from the hydrolysate of insoluble residues) and l-ascorbic acid were degraded to determine distribution patterns of 14C within the carbon chains. Results indicate that d-[5- 3H,1- 14C]glucosone is a better source of 14C for oxalic acid while d-[5- 3H,6- 14C]glucosone is a better source of 14C for l-tartaric acid, findings supportive of the view that l-ascorbic acid is intermediate in the overall conversion of d-glucosone to oxalic acid and tartaric acid. Loss of 3H from C-5 of d-glucosone occurs during this process, an indication that epimerization at this site involves labilization of the hydrogen-carbon bond.
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